Consolidated Statements of Cash Flows Supplemental Disclosures (Non-cash Investing and Financing Activities) (Details) - USD ($) $ in Thousands |
9 Months Ended | |
|---|---|---|
Sep. 30, 2017 |
Sep. 30, 2016 |
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| Supplemental Cash Flow Elements [Abstract] | ||
| Non-cash additions for purchases of property and equipment | $ 13,676 | $ 11,372 |
| Net asset retirement obligation additions (deletions) to property and equipment | $ 986 | $ (2,279) |
| X | ||||||||||
- Definition Future cash outflow to pay for purchases of fixed assets that have occurred. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- Definition The increase (decrease) during the reporting period in the carrying amount of asset retirement obligations. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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| X | ||||||||||
- References No definition available.
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